Stopcocks have long been used to meter fluids. A core with an internal passage is received in the bore of a valve body, and rotation of the core by means of an attached handle brings the internal passage into or out of communication with fluid passages in the valve body. A close fit must be achieved between the bore and core so as to minimize leakage while allowing for unimpeded core rotation. In stopcocks assembled from molded thermoplastic parts, distortions in the shape of the bore introduced during cooling contribute to sealing deficiencies unless compensated for by increased fit interference between the core and bore. Greater interference, however, leads to undesirably high turning torque for the core. The distortions are the result of nonuniform rates of cooling of different portions of the valve body. External fittings generally solidify first, and the natural shrinkage occurring on cooling tends to draw still-molten material away from the valve body, thereby leaving sinks or depressions in the bore opposite the fittings.
A stopcock manufactured by Pharmaseal, Inc., Glendale, Calif., comprises a molded tubular valve body and a core held together by a friction cap pressed onto one end of the core after its installation through the valve body. Integral fittings are secured to the exterior of the tubular body, and the core and tubular interior of the valve body are both slightly tapered to allow the slightly larger core to achieve an interference fit with the body when the two pieces are axially forced together.